1. Field of the Invention
The present invention relates to a color photographic material, and more specifically to a silver halide color photographic material where silver halide of a comparatively small grain size is used and sensitivity, graininess and sharpness are improved.
2. Description of the Prior Art
There have been many studies which were made in an effort to enhance sensitivity of color photographic materials and to improve the quality of a reproduced color image. In addition, the improvement of the stability of color photographic materials during storage has also been sought.
Generally, the larger the size of silver halide grains becomes, the higher the sensitivity of silver halide light-sensitive material becomes. However, the quality of the reproduced color image decreases as the size of the grains increases. That is to say, in light-sensitive materials in which silver halide grains of a large grain size are used, entering light is reflected or refracted by the emulsion grains during exposure, which makes the sharpness of the image extremely poor. Particularly, if the grain size in an emulsion layer in a layer furthest from a substrate is large, the underlying layers (i.e., green-sensitive layers and red-sensitive layers) are adversely affected. Accordingly, it is impossible to adopt the method of using grains of a large size in order to the enhance sensitivity of the uppermost emulsion layer.
Meanwhile, many studies have been made concerning methods for enhancing the sensitivity without increasing the grain size. A method of using a sensitizing dye is known as one of such methods. Although this technique of using the sensitizing dye is quite useful for sensitization, it has many problems which need to be solved. For instance, (1) sufficient sensitivity is sometimes not obtained depending on the size of emulsion grains; (2) storage stability is not sufficient after the addition of the sensitizing dye, so that the sensitivity decreases or fogging takes place with time; and (3) in the event that the spectral absorption range of the sensitizing dye is not proper, color mixing is observed in a reproduced color image. Particularly when the size of the grains in the emulsion is small, the above disadvantages become further serious because the surface area of the grains per unit volume and accordingly the amount of the used sensitizing dye becomes larger.
For the above reasons, the combinational use of a fine grain emulsion, in particular of average grain size of 0.4 micron or less and a sensitizing dye has scarcely been studied.